VoIP Chips: How SLICs and Codecs Connect Analog Phones
Yenra | Prepared October 3, 2026
Guide: https://yenra.com/voip-chips/

LINE-CIRCUIT DATASHEET READING WORKSHEET
For technical reading and qualified design review; not a live wiring procedure.
Start with the exact part and complete manufacturer's reference design.

Part / revision / datasheet URL / date / lifecycle status:
Port count and role: FXS, FXO or another interface?
Line feed, ringing and supervision: block / datasheet section:
Analog-to-digital and digital-to-analog conversion: block / section:
Filtering and supported coding formats: block / section:
Sample interface / control interface / clocks / host compatibility evidence:
External supply and protection requirements / reference design:
Host software responsibilities: call signaling, media, buffering, management:
Driver/API and profile support / errata / maintenance owner:
Unresolved function or interface / owner / evidence needed:

FUNCTION MAP
Analog phone -> line interface -> conversion/filtering -> host -> packet network
Mark each function as on-chip, separate hardware or software. Return audio takes
the reverse functional path. Actual package boundaries depend on the design.

FICTIONAL EXERCISE AND ANSWER
A two-port gateway proposal names a host SoC and a SLIC. Where is conversion?
Answer: inspect the selected part. A combined SLIC/codec can provide conversion;
a SLIC-only choice needs an identified separate conversion path. Record how
samples and control reach the host before proceeding to pin-level design.

In a hardware datasheet, codec can include conversion and coding functions.
Verify the exact formats instead of assuming all softphone codecs are supported.
Use supported equipment diagnostics; electrical line testing requires qualified
personnel, appropriate instruments and the manufacturer's procedures.

Supporting sources (see guide for context):
https://www.microchip.com/en-us/products/power-management/line-circuits
https://www.maxlinear.com/products/interface/voice/telephony-chipset-for-cpe
https://www.microchip.com/content/dam/mchp/documents/LCLD/ProductDocuments/DataSheets/Microsemi_Voice_Line_Circuits_Le9642_Data_Sheet_V8_PD-248193%28web%29.pdf
https://www.rfc-editor.org/rfc/rfc3261.html
https://www.rfc-editor.org/rfc/rfc3550.html